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Specificities of actions of fucoidanases from the marine microorganism Pseudoalteromonas citrea KMM 3296 and the marine mollusk Littorina kurila were studied. The enzymes possess similar specificities and catalyze the cleavage of accessible α-(1→3)-fucoside bonds in fucoidans with highly sulfated α-(1→4; 1→3)-L-fucooligosaccharides. A high degree of sulfation of the fucose residues in fucoidans makes α-(1→3)-L-fucoside bonds inaccessible for the action of the studied enzymes. The maximum degree of cleavage of fucoidan was achieved by the fucoidanase from the marine bacterium Pseudoalteromonas citrea KMM 3296.

On the extensive sedimentary tidal flats of the Wadden Sea, beds of the blue mussel Mytilus edulis represent the only major hard substratum and attachment surface for sessile organisms. On this substratum, the barnacle Semibalanus balanoides is the most frequent epibiont. In summer 1998, it occurred on over 90% of the large mussels (>45 mm shell length) and the dry weight of barnacles reached 65% of mussel dry weight. However, the extent of barnacle overgrowth is not constant and differs widely between years. Periwinkles (Littorina littorea) may reach densities >2000 m−2 on intertidal mussel beds. Field experiments were conducted to test the effect of periwinkle grazing on barnacle densities. An experimental reduction of grazing and bulldozing pressure by periwinkles resulted in increased recruitment of barnacles, while barnacle numbers decreased with increasing snail density. The highest numbers of barnacles survived in the absence of L. littorea. However, a lack of periwinkle grazing activity also facilitated settlement of ephemeral algae which settled later in the year. Field experiments showed that the growth rate of barnacles decreased in the presence of these ephemeral algae. Thus, L. littorea may reduce initial barnacle settlement, but later may indirectly increase barnacle growth rate by reducing ephemeral algae. It is suggested that periwinkle density may be a key factor in the population dynamics of S. balanoides on intertidal mussel beds in the Wadden Sea.

Intertidal areas are habitats at the border of two very different environments: the marine environment and the terrestrial environment. In contrast to many habitats at borders, intertidal areas are very variable in space and time. They have upshore and alongshore gradients of environmental conditions, which change through time in predictable (due to changing tides) and unpredictable (due to changing weather) ways. Because most animals and plants on rocky shores are marine in origin, extreme highshore levels are generally considered more harsh and unpredictable environments than are mid- or lowshore levels. In this study, the linear distances and directions dispersed by the littorinid Littorina unifasciata while foraging were compared across randomly-chosen mid- and highshore replicated sites to test the hypothesis that movement during foraging was more variable from place to place in complex midshore habitats. Experiments were repeated on different days to test the hypothesis that temporal variability in movement was greater at high- than at midshore levels because environmental conditions necessary for foraging were more variable high on the shore. Finally, the data were used to test models about differences in variability among individuals in the same patch of habitat according to their recent history of submersion/emersion. In contrast to expectations, dispersal was more variable in space and time within and among highshore sites. The implications of such variable behaviour are discussed with respect to the generalization of patterns of behaviour from sparse data and the levels of replication needed in the design of experiments to investigate behaviour of intertidal animals.

In Amakusa (Japan), an apparently homogeneous population of Littorina brevicula, divides into two groups during the reproductive season (winter). Some snails migrate to the lower intertidal zone, while the rest remain in the upper zone. This migration behaviour might be controlled genetically and the behavioural dimorphism may be maintained by assortative mating. To evaluate this hypothesis, we studied genetic variation at four polymorphic enzyme loci (Pgm, Aldh, Ipp, Gpt) in both groups, as well as in seven other samples from the coast of Japan and Vostok Bay (Russian coast of the Sea of Japan). There were no significant allele frequency differences between the two behavioural groups of snails with differing migration patterns (χ 2 = 8.411, df = 12, p > 0.5). The samples from Japan belong to a panmictic population. Yet, a significant heterogeneity was found between the sample from Vostok Bay and the samples from Japan, indicating a reduced gene flow between these regions. Generally, observed genotype frequencies showed good fits to Hardy-Weinberg equilibrium expectations at three of the four loci investigated.

Using isoelectric focusing of esterases (EST), general proteins (GP) and myoglobin (Mb), we surveyed intra- and interspecific differentiation in flat periwinkles along a vertical intertidal transect in the Ensenada do Bano at Ria Ferrol, N.W. Spain. In this region, L. obtusata occurs in four algal belts, although it is rare in the lowest zone defined by Fucus serratus. L. fabalis is common in the F. serratus and F. vesiculosus belt, but is absent higher up on Ascophyllum nodosum and F. spiralis. Our data show that (1) EST and GP consistently differentiate between L. obtusata and L. fabalis, without however providing useful diagnostic markers, (2) L. fabolis is the less variable (heterozygous), but more heterogeneous species, (3) Mb patterns show significant heterogeneity in L. obtusata between the F. serratus zone and the other algal belts, but not in L. fabalis, and (4) the data on littorinid Mb appear inconsistent with a dimeric protein controlled by a single locus. Yet, assuming two loci coding for a monomeric (or dissociated dimeric) protein produces for the flat periwinkles a data set in which no significant deviations from Hardy-Weinberg expectations were detected. Nevertheless, this speculative interpretation fails to explain all littorinid Mb data. Hence the genetics and structure of littorinid Mb need further study.

Two different tributyltin (TBT)-induced virilisation phenomena in prosobranch snails — intersex in Littorina littorea and imposex in Nucella lapillus — are compared in order to facilitate their simultaneous use in geographical large scale effect monitoring surveys. Imposex in dogwhelks is a more sensitive biomarker and should be used in areas that are only slightly or moderately contaminated with TBT (ambient TBT concentrations < 2.0 ng as Sn 1−1). The assessment of intersex intensities in periwinkle populations has considerable advantages in areas with higher TBT concentrations and should be used also wherever dogwhelks are absent irrespective of the TBT exposure level. The intersex index (ISI) and vas deferens sequence (VDS) index are proposed as the most suited parameters for effect monitoring purposes. The geographical uniformity of intersex and imposex is analysed and proven for the coasts of Ireland, France, and Germany. A relative loss of TBT sensitivity in females can be found, but to a varying extent in both species. The implications of this result for biological TBT effect monitoring programmes are discussed in light of the fact that intersex and imposex have both been found to be irreversible. Because it is the objective of these programmes to assess current TBT contaminations and resulting biological effects, only relatively young specimens should be considered in the sampling strategy.

A short description of the imposex condition in Hydrobia ulvae is presented. In this species four different imposex stages with two types of development were identified. In laboratory experiments the mud snail accumulates TBT in a time and concentration-dependent manner. Increasing biological indices e.g. VDSI (vas deferens sequence index), female penis length (FPL) and the imposex incidence are significantly correlated with increasing TBT body burden. The percentage of sterile females depends on the TBT contamination of sediments. An interspecific comparison of the mud snail H. ulvae and the periwinkle Littorina littorea elucidates that the mud snail is the more sensitive species at lower environmental TBT concentrations.

Cork Harbour, located on the south coast of Ireland, is a complex, multi-user environment. In the present study Littorina littorea (L.) is used as a bio-indicator of TBT pollution, as it has a wide range within the harbour, unlike the more common bio-indicator, Nucella lapillus (L.), which is limited to rocky substrata near the mouth of the harbour. Intersex in L. littorea is used for the first time in Ireland as a medium-term indicator of TBT pollution and results show that there are no deviations in levels of intersex over the three year period from 1994–1996. These results are discussed.

The radular muscles of several littorinid species, including Littorina littorea, L. saxatilis, L. obtusata, L. striata and Melarhaphe neritoides, contain myoglobin (Mb). Here we report on the presence of radular Mb in eight other littorinids: L. compressa, L. arcana, L. fabalis, Nodilittorina punctata, N trochoides, N. radiata, Littoraria undulata and Littoraria cingulifera. Using native Polyacrylamide gel electrophoresis (PAGE) and isoelectric focusing (IEF) we compared the Mb and soluble protein (SP) profiles of these species. This suggested that: (1) L. saxatilis and L. arcana may have specific Mb/SP profiles, (2) Littoraria spp., Nodilittorina spp. and L. striata share similar Mb patterns, (3) Mb is remarkably diverse in the genus Littorina, (4) L. littorea shows intraspecific Mb/SP variation, (5) L. saxatilis does not show geographic Mb/SP differences, and (6) IEF uncovers substantial hidden Mb/SP heterogeneity not shown by PAGE (particularly for Melarhaphe neritoides). Hence, littorinid Mb/SP may be a useful taxonomic marker whose ecophysiological significance deserves further study, even if its genetic basis remains unclear.

Littorina tenebrosa is a small fragile-shelled periwinkle which lives on permanently submerged algae in coastal lagoons and non-tidal brackish pools. This periwinkle is a member of the rough periwinkle group which also comprises Littorina saxatilis, L. arcana, L. compressa and L. neglecta and is most closely related to L. saxatilis although its exact systematic status is in some doubt. Based on its unique ecology many believe L. tenebrosa to be a valid species. However, shell morphometric and allozyme analyses on Scottish and Swedish populations of L. tenebrosa and L. saxatilis have indicated that the two periwinkles are virtually identical. Preliminary results on five allozyme loci (AAT-1, GPI, PGM-1, PGM-2 and PNP) in samples of L. tenebrosa and L. saxatilis from Golam Head, Lettermullen, and other locations on the west coast of Ireland show L. tenebrosa to be genetically differentiated from L. saxatilis. At Golam Head, where opportunities for gene flow occur between the two taxa, L. tenebrosa is as genetically differentiated from local L. saxatilis as it is from L. saxatilis from more geographically distant locations.

Gills were examined in Littorina saxatilis, L. arcana and L. neglecta, using animals of similar size. The form of the gills in the three groups is very similar, although there is an indication of qualitative differences between them. The relationship of number of gill lamellae to shell length shows that L. saxatilis and L. arcana share the same allometric relationship, while in L. neglecta the slope is the same but the intercept is less: at equivalent shell sizes, these animals have about three fewer lamellae.

The relationship between gene flow and the maintenance of geographic or morphology-related variation in the polymorphic Macaronesian periwinkle, Littorina striata, was investigated by means of isoelectric focusing of esterases (EST) and myoglobin (Mb). This revealed that: (1) individual EST variation is very high, (2) there is no EST differentiation between sexes, shell morphotypes or wave-exposure regimes, (3) there is no clear macrogeographic patterning of EST variability, although both Cape Verde Islands have the highest, with exception of Flores, mean number of EST bands, and (4) there is no Mb variation, not even between islands separated by more than 2000 km. These results indicate that L. striata shows a high degree of genetic homogeneity among geographic populations and that the morphological patterning in this species persists in the presence of intense gene flow.

The ecological implications of parasitism of Littorina littorea (L.) (Gastropoda: Prosobranchia) and other gastropods by larval digenean trematodes has attracted considerable research interest (e.g. Lambert & Farley, 1968; Williams & Ellis, 1975; Lauckner, 1987; Sokolova, 1995). Such implications hinge on an accurate quantification of parasite loading within an infected population. There are several techniques available for determining parasite load or an index of it. Dissection, usually of the digestive gland, is the most commonly used destructive technique (e.g. Williams & Brailsford, 1990; Granovitch, 1992; Siddal et al., 1993), which can give an accurate estimate of parasite load in terms of the number of cercariae present. The subjective ‘foot colour’ technique correlates the intensity of orange colour of the foot of L. littorea to the degree of infection by Cryptocotyle lingua (Creplin) (Digenea: Heterophyidae), (e.g. Willey & Gross, 1957; Huxham et al., 1993), however, dissection should be employed to investigate the presence of other trematode cercariae.

Starch-gel electrophoretic techniques were applied to the investigation of molecular genetic variation in populations of the rough periwinkle Littorina saxatilis. The investigation comprised two phases: (a) technique development to resolve as many as possible of the allozyme loci reported in the literature as having been screened in the genus Littorina and in Melarhaphe neritoides; (b) the use of these loci to assess levels of genetic variation in and patterns of genetic differentiation among populations of L. saxatilis from a relatively isolated group of populations from Galway Bay, Ireland.

A population of Littorina littorea on the north shore of Southampton Water, UK, has been examined for the occurrence of epifauna. Epifaunal cover was not affected by shore level below MTL but was greatest on larger shells, which were commoner on the lower shore close to MLWS. Epifaunal components included barnacles, serpulids and bryozoans. The polychaete Polydora ciliata occurred most frequently on the lower shore where it excavates galleries in periwinkle shells. Heaviest infestations were found in larger shells. P. ciliata settles preferentially in or beside irregularities on the shell surface. Settlement of barnacles close to the shell aperture, where new shell growth takes place, produces shell distortion which creates sites for settlement of R ciliata. The angle between serpulid tubes and the shell surface also attracts P ciliata. It is suggested that colonisation by barnacles and serpulids facilitates settlement by R ciliata, and that the latter decreases survival of the host by progressively destroying the shell.

Two field experiments were carried out to test whether effects of intraspecific competition in a Littorina littorea population can be detected in a short-term investigation. Different size classes of L. littorea showed no significant difference in preferences when offered four kinds of either possible food or substrata (Fucus vesiculosus, Ulva lactuca, Carcinus maenas, brick). Large and medium winkles preferred Fucus vesiculosus, followed by Ulva lactuca. Dead shore crabs (Carcinus maenas) were the least preferred objects for all size classes. On the first day of the experiment bricks were more attractive to small littorines than to larger ones. Considering all four days, the same ranking occurred for all size classes: Fucus vesiculosus> Ulva lactuca>brick > Carcinus maenas. The reaction of juveniles to increased densities was examined using an in situ caging experiment on a mussel bed. Mesh size of the cages allowed adult densities to be increased while juveniles could escape by passing through the meshes. However, there was no significant emigration of small winkles even from cages with 10 to 20 times natural density of large individuals. Of greater importance was the original number of winkles at the site. The available resources on the mussel beds appear to be sufficient to maintain a high population density. Intraspecific competition does not seem to play a major role in this L. littorea-population.

Marine gastropods which do not disperse larvae in the plankton exhibit a relatively high degree of interpopulation morphological variability. This phenomenon has been the root of considerable taxonomic confusion, particularly in the Littorinidae. In the present study, specimens of Littorina obtusata from the UK were compared morphologically and genetically with two samples of a northern high-spired form from Iceland which has been referred to by some workers as Littorina palliata. A multivariate discriminant function analysis based on three measured shell dimensions clearly separated the three samples, correctly predicting the origin of shells on the basis of morphology alone in 96% of cases. However, genetic analysis revealed that the most distant relationship, based on allozyme data at 13 loci, was surprisingly close (Nei’s I=0.983) providing no evidence to suggest that L. palliata is not conspecific with L. obtusata.

Eight species of the genus Littorina were hitherto recognised in the north-western region of the Pacific Ocean: L. sitkana, L. brevicula, L. mandshurica, L. squalida, L. aleutica, L. naticoides, L. kasatka and L. subrotundata. Using allozyme electrophoresis it has been demonstrated that, in the Kurile Islands, three of these species (L. sitkana, L. subrotundata and L. kasatka) co-occur, together with a fourth, still undescribed species (L. sp.). These four species were compared at 16 loci coding for 13 enzymes. All species were easily distinguished by diagnostic enzyme markers. The mean genetic distances and ranges between species pairs are: L. sitkana and L. sp. D = 0.622 (0.561–0.741), L. sitkana and L. subrotundata D=0.981 (0.821–1.110), L. subrotundata and L. sp. D=0.975 (0.955–0.995). The genetic distance between L. kasatka and each of the other three species was greater than 1 (range 1.123–2.087). These data suggest that L. sitkana, L. subrotundata and L. sp could be members of a species complex; according to current classifications these three belong to the subgenus Neritrema. However, the genetic distance between L. kasatka and L. sitkana is much greater than between L. sitkana and other Neritrema species, and thus supports the classification of L. kasatka in the subgenus Littorina.

This study forms part of a larger project in which five planimetric parameters have been used to study changes in the digestive epithelium of Littorina littorea under different environmental and physiological conditions. Our aim was to examine the effect of the reproductive cycle on these parameters in order to assess their usefulness as indicators of stress. A one way anova shows that the absolute parameters of mean epithelial thickness (MET), mean diverticulum radius (MDR) and mean luminal radius (MLR) vary significantly depending on the time of the year. This variation is highly correlated to the amount of digestive tissue present and hence negatively correlated to the reproductive state because gonad and digestive tissue volume are inversely related. Consequently, these parameters are not good indicators of stress. However, whereas the absolute size of the digestive acinus varies with the reproductive state of the animal, the MET, MDR and MLR retain the same proportions and therefore the ratios MET/MDR and MLR/MET remain constant. This makes them useful indicators of stress because they are independent of intrinsic variables such as the reproductive cycle.

Alpha-autoradiographic and radiochemical techniques were applied to mussels (Mytilus edulis), winkles (Littorina littorea) and Dublin Bay prawns (Nephrops norvegicus) radiolabelled under both laboratory and environmental conditions in order to assess the differences and similarities in radionuclide accumulation. In the laboratory, the marine organisms were exposed 237Np, 239Pu and 241Am using food and water labelling media. In general, tissues and organs associated with digestion had greater radionuclide accumulative properties than other soft tissues. The most intense α-track distributions were found, however, in the winkle’s chitinous operculum. Other markedly active tissues were the viscera of the mussel and winkle, the pallial complex of the winkle and the hepatopancreas of the prawn, each of which exhibited varying degrees of heterogeneity in their α-track distributions. Laboratory experiments show that the accumulation and distribution of transuranic radionuclides in marine invertebrates are highly influenced by the presence of scleroproteins, chitinous material and mucous secretions.

The status of the four currently recognised species in the Littorina saxatilis species-complex, i.e. Littorina nigrolineata Gray, L. arcana Hannaford Ellis, L. saxatilis (Olivi) and L. neglecta Bean is reviewed briefly, with notes on their characteristic features and location on the shore. Since the taxonomy of these rough periwinkles has only become stable relatively recently much of the previously published information on distribution is of little or no use. In this paper their distribution around the coastline of England and Wales (with some notes on Scotland) is described and discussed. L. saxatilis is found in a wide range of habitats from exposed peninsulas to estuaries on all shores where there is a suitable rocky or stony substrate; also in salt marsh pools. L. arcana has a more restricted distribution and is notably absent along much of the south English coast, central Cardigan Bay and possibly northern Scotland; it is not found in estuaries. L. nigrolineata has an even more restricted distribution, although it occurs both on exposed coasts and in estuaries; it has only been found by us in one locality on the east coast. L. neglecta is probably fairly widely distributed but we have few details so far. The implications of the different patterns of distribution are discussed.

The Belgian coast has no natural rocky sites but a number of man-made constructions are colonized by rocky shore organisms. The rough periwinkle, Littorina saxatilis (Olivi), lacks a planktonic larval stage but is found on most breakwaters along the Belgian coast, a few built as recently as 1986. This indicates a good potential of dispersal along this sandy shallow coast, nearly as good as for the planktonic developer Littorina littorea (L.) which is found on generally the same sites in Belgium. The breakwater populations of L. saxatilis, however, tend to be somewhat less variable (level of heterozygosity about 10% less) than non-Belgian L. saxatilis populations of natural sites. This suggests that the breakwater populations have passed through bottlenecks when founded, but probably restored population sizes fairly rapidly afterwards. No relationship is found between geographic and genetic distances between populations of L. saxatilis.

The ability of males of Littorina littorea and L. saxatilis to discriminate between mates of different sex, species and size was examined. In partner choice experiments males of L. littorea had the possibility to initiate a copulation with either a female or a male. The males did not show a preference for either sex. There was therefore no evidence that they could determine the sex of a conspecific prior to copulation. The duration of intrasexual copulation was considerably shorter than for intersexual copulation, both in the field and in laboratory experiments. For the two species, intersexual copulations were far more frequent than intrasexual ones. This can partly be explained by the difference in copulation time.

The morphological variation of Littorina saxatilis and L. neglecta on a microscale (vertical transects down a shore) and on a geographical scale (Northeastern Atlantic) was examined to see if the sampled snails could be consistently separated into two groups on morphological criteria. Size, shell form and shell banding pattern, subopercular pattern and size at maturity were recorded for 21 samples from different shore levels (barnacle zone — usual habitat of L. neglecta, low littoral fringe and high littoral fringe — usual habitat of L. saxatilis) in Iceland, Norway, Sweden, Isle of Man and Wales. A multivariate approach (principal component analysis) was applied to analyse 14 quantitative shell characters. Between-shore variation in shell shape of samples from similar levels was generally larger than within-shore variation of samples from different levels, while size of snails was consistently smaller in barnacle zone compared to littoral fringe samples. The frequency of snails with qualitative characters, used in earlier studies to define L. neglecta, differed between samples from the littoral fringe and the barnacle zone at each site (except at the Swedish site), but the differences between geographical areas were generally larger. The results indicate that snails fitting earlier descriptions of L. neglecta are present in the barnacle zone in Iceland, Norway, Isle of Man and Wales, but that this form is not clearly distinguishable from L. saxatilis. Snails with intermediate shapes were common and, furthermore, the qualitative and the quantitative characters used to define L. neglecta were not closely coupled. No snails of L. neglecta form were found at the Swedish site, yet shape differences over the intertidal gradient were greatest at this site.

Rough periwinkles are notoriously variable in shell characters. There are many reports of substantial local variation on single shores which not only make identification difficult but also may be difficult to understand in terms of likely selective pressures. We show that despite local variation in southern Britain there is evidence of a broader scale of change which is likely to be explicable in adaptive terms. At the same time, along an extreme environmental gradient on a single shore in south Wales we show that there are changes in morphology which are related to avoidance of water loss.

Feeding responses of the generalist herbivore, Littorina littorea (L.), to the perceived ‘taste’ of macroalgae were assessed with respect to the effects of recent dietary intake and to overlapping versus non-overlapping distributions of winkles and algae. The extent of grazing on artificial substrates impregnated with crude algal extracts was used as a measure of rate of response to the odour of preferred algae, and of feeding preference among less preferred algae, in a variety of designs. Adult L. littorea collected from a site where a range of algae were present showed preference among extracts of fucoids, whereas adults from a nearby site showed no such preference. Juvenile L. littorea of two weight cohorts collected from the former site responded faster to Porphyra umbilicalis extract-containing substrate than similar-sized animals from the latter site. Juveniles, fed either Porphyra, Ulva lactuca, or starved for two weeks in the laboratory, responded similarly to Ulva versus Porphyra extracts in a dose-dependent manner across a range of concentrations, although the Porphyra-maintained group consumed more of each, and the starved group less over seven days. Juveniles maintained on a mixed diet of Ulva and Porphyra consumed more Porphyra extract and less Ulva extract over the same period. These results are discussed in relation to the possible role of ingestive conditioning and previous dietary history in determining the occurrence and extent of chemically-mediated feeding preference in L. littorea.

Genetic variation was compared within- and between-samples of Littorina saxatilis and L. neglecta from five geographic regions of western Europe (Iceland, Norway, Sweden, Isle of Man and Anglesey). The variation at five highly polymorphic enzymes (Aat-1, Pgm-1, Pgi, Mpi and Np) were revealed in samples from eleven vertical transects extending upshore from the barnacle zone to the upper littoral fringe. Both morphological types, L. saxatilis and L. neglecta, were present in all geographic regions except in Sweden.

Gross anatomical characters of all 18 species of Littorina are used to construct a phylogenetic hypothesis for the genus, by the method of cladistic analysis. The resulting cladogram suggests that of the four subgenera of Littorina,one (Littorina) is paraphyletic. It is uncertain whether the genus Mainwaringia should be included in Littorina. It is shown that the non-planktotrophic Littorina species in the northern Atlantic comprise a monophyletic group, with the sister-species L. kurila and/or L. subrotundata in the northern Pacific. Invasion of the Atlantic by a minimum of two Pacific species, across the Arctic migration route established during the late Cenozoic, is sufficient to account for the modern distribution of the subgenera Littorina and Neritrema. The importance of the cladogram as a basis for hypotheses of adaptation is illustrated by a discussion of spawn and development in Littorina.

The genus Littorina has been subject to many studies of electrophoretically detectable variation, mostly aimed either at clarifying questions concerned with population structure, or at clarifying difficult taxonomic/systematic problems. This paper reviews many of these studies. Topics covered include Hardy-Weinberg deviations, the extent of genetic differentiation among populations within species, founder effects and the effects of human introductions on genetic variation, the biological significance of allozyme variation, and the uses of allozyme variation in Littorina systematics.

An examination of the shell microstructure and mineralogy of species from 30 of the 32 genera and subgenera of the gastropod family Littorinidae shows that most species have a shell consisting of layers of aragonitic crossed-lamellar structure, with minor variations in some taxa. However, Pellilitorina, Risellopsis and most species of Littorina have partly or entirely calcitic shells. In Pellilitorina the shell is made entirely of calcitic crossed-foliated structure, while in the other two genera there is only an outer calcitic layer of irregular-prismatic structure. A cladistic analysis shows that the calcitic layers have been independently evolved in at least three clades. The calcite is found only in the outermost layers of the shell and in species inhabiting cooler waters of both northern and southern hemispheres. Calcium carbonate is more soluble in cold than warm water and, of the two polymorphs, calcite is about 35% less soluble than aragonite. We suggest that calcitic shell layers are an adaptation of high latitude littorinids to resist shell dissolution.

In previous work we have studied the uptake and distribution of technetium in several marine organisms, including microbial species, unicellular and pericellular algae and molluscs [1–5]. The experimental work on technetium uptake by molluscs (Littorina littorea, Mytilus edulis, Patella caerula and Patella vulgata) was continued. In addition, investigations were realised on the marine fish Serranus cabrilla, contaminated with 99Tc-pertechnetate (direct contamination) or fed with labeled molluscs (indirect contamination).

The variability of Actinocyclus kuetzingii (A.S.) Sim. in the Littorina deposits of the Vistula Lagoon and Lake Druzno were studied. During the time of the Littorina Lake Druzno was a part of the Vistula Lagoon. In the different parts of the Lagoon both the abundance of A. kuetzingii and the diameter of its valves change in a manner associated with phases of the Littorina transgression. Coscinodiscus (Actinocyclus) kuetzingii fo. subsalsa Brockmann is probably an ecotype of A. kuetzingii (A.S.) Sim.

Along the coast of St. Martin, St. Eustatius and Saba the rocks above sea-level often show a number of differently coloured zones. This is clearly visible when the coast over a larger distance is formed by one type of rock, as for instance on Saba. In many places a light-coloured belt is seen above the zone with algal growth; still higher the rocks are dark-coloured (Fig. 11, 17 and 22). The uppermost part of the light-coloured zone indicates rather exactly the height of the waves at low tide (splash zone). The darkcoloured zone is wet from finely dispersed water (spray zone). Sometimes differently coloured zones are formed (Fig. 13) which may, however, be correlated with the above mentioned ones on account of their organisms. Below the algal zone on open coasts hardly any other zones can be discerned, since the various communities of plants and animals form here a mosaic-like pattern. On rocky bottoms in the sublittoral region next to the lithophilous algae many corals are present. When the rocks are covered with a thin layer of sand, a rich fauna of Gorgonids may be present; when this layer becomes thicker, the horny corals are replaced by seagrasses and psammophilous algae. From our data the following facts about the rocky coasts, from the supralittoral margin to the uppermost part of the sublittoral region, are obvious. A zonation for molluscs is distinctly visible. Tectarius tuberculatus and Littorina ziczac are found in the spray zone, which is usually recognizable by a dark colour, caused by microscopic bluegreen algae. The rocks in this zone as a rule are almost dry. Chitons are usually present at a somewhat lower level, in places which are constantly washed by the waves; generally they indicate the upper limit of the waves at low tide (e.g. Figs. 17 and 21). They are mostly found in a lightcoloured zone. In places where the rocks are not exposed to the sun, Chitons may occur at much higher levels than is normally the case, when, however, the rocks are scoured by sand they are scarce or absent